María Victoria Bueno Delgado

Single antenna physical layer collision recover receivers for RFID readers

Radio Frequency Identification (RFID) systems often are operated in environments with multiple RFID tags. In such an environment, a conventional RFID system resolves collisions of multiple tags on the medium access control layer, discarding the signals of the physical layer. This paper proposes a zero-forcing and an interference cancellation receiver architecture for an RFID reader, to recover from collisions of two tags on a physical layer and identify tags successfully even in case of a collision. The expected throughput increase is approximately 1.6 times the throughput of a conventional reader. We explore the signal properties of collisions and propose a model for the physical layer. Moreover, we present a method for estimating the signal constellation states in a collision. The entire structure, including channel estimation and both of the proposed receivers are verified with data generated during a measurement. Additionally, performance simulations of the two structures with different channels are shown.

Using Non-uniform Probability Distribution p* to Improve Identification Performance in Dense RFID Reader Environments

This paper proposes the use of the non-uniform probability distribution function to improve the performance of passive UHF RFID systems with several readers. In a previous work, the authors proposed GDRA, a mechanism based on the NFRA protocol where the readers used a truncated geometric distribution function to select a contention slot, instead of the typical uniform distribution function. Results showed that GDRA increased the RFID system performance but, this improvement could be higher if the optimal non-uniform probability distribution function is used. In This was not possible due to the inability of readers to calculate the number of (interfering) neighboring readers, a necessary parameter to apply it. This work solves this issue, using a mechanism where readers calculate the average number of neighboring readers through a simple formulation extracted from graph theory unit disk applied to wireless sensor networks.